Numerical analyses on oxygen transport resistances in polymer electrolyte membrane fuel cells using a novel agglomerate model

Characterizing oxygen transport resistances in different components of a polymer electrolyte membrane fuel cell (PEMFC) is essential to achieve better cell performance at high current under low Pt loading. In this work, a macroscopic three-dimensional model, together with a novel agglomerate model was proposed to analyze impacts of operating conditions on these resistances via limiting current strategy. By introducing a focusing factor obtained with lattice Boltzmann method at mesoscopic level, the structure-dependent local transport resistance in ionomer thin-film of the electrode was comprehensively captured and validated by existing experimental studies. Contributions of the cell components to the total transport resistance were dissected. Results show that the present agglomerate model could well reproduce the local transport behaviors of oxygen in catalyst layer by fully considering the detailed nanoscale diffusion and adsorption processes. A small mass fraction of oxygen was favored to minimize the relative deviation of the local transport resistance from its intrinsic one due to the water production and heat generation, which can reach 7% for the mass fraction of oxygen of 1%. Contribution of the in-plane diffusion of oxygen in the inactive electrode is around 1%. The total transport resistance increased with the absolute pressure, mainly due to the dominated mo-lecular diffusion mechanism in gas channel and gas diffusion layer. Gas convection accounted for 26% of the oxygen transport resistance originated from gas channel. The transport resis-tance of catalyst layer increased significantly with the reduction of Pt loading, and decreased with relative humidity and operating temperature, particularly at high Pt loading.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

Characterizing oxygen transport resistances in different components of a polymer electrolyte membrane fuel cell (PEMFC) is essential for achieving better cell performance. The proposed macroscopic three-dimensional model and agglomerate model help analyze the impacts of operating conditions on these resistances. The study provides insights into the structure-dependent local transport resistance in the electrode and the contributions of different cell components to the total transport resistance. Understanding and optimizing oxygen transport in PEMFCs are crucial for improving their efficiency and performance.